2
SEC Ref #: S11-64-H2OPOWER

Renewable energy is energy that is created by utilizing any natural resource that is easily and frequently replenished. Currently, renewable energy is used as an alternative to nonreplenishable methods such as coal or oil. Last year renewable energy production accounted for nearly 20 % of the total energy consumption across the planet. Thirteen percent came from biomass, or the production of energy from the use of wood, waste, hydrogen gas, and alcoholbased fuels. Three percent came from hydroelectric power such as dams and other current water propelled systems. The remainder can be attributed to other smaller yet vastly growing sources such as, solar power, geothermal, and biofuels [12] .
With such a wide variety of renewable energy systems and sources, many often get overlooked. One example of this is hydroelectric energy. Conventional systems like dams use the potential energy of water to drive a turbine and generator; however there are also tide and river run hydroelectric energy generation systems.
While all of these sources of energy are essential to furthering the process of using all environment friendly energy production, some systems have more potential than others. Wind power is the fastest growing renewable energy source and grows at a rate of 30 % annually, and while solar energy provides a great potential it only converts 7-8 % of the potential energy that is provided [12]. A sample calculation was prepared to show the potential amount of electricity that could be made from rain. The sample building has a roof that is 10,000 ft 2 and 100 meters tall.
One inch of rainfall on this roof would be equal to 833 (10,000 ft
2
*.08333 ft) cubic feet of water, which is equal to 6230.84 (833 ft
3
* 7.48 gal/ft
3
) gallons. The potential energy of the water would then be equal to the mass of the water times the height of the building times the gravitational constant 9.81m/s
2
. The mass of water equals 23,583.7294 (6230.84 gal* 3.785 kg/gal) kilograms. Multiplying these numbers gives us 23,135,638.54 joules of energy. Dividing this result by 3600 seconds in an hour and again by 1000 equals 6.4266 kilowatt hours.

Rainfall Data
Precipitation data for the United States and across the world shows that there are many opportunities to use rainfall as a power source. Places like the Pacific Northwest coast, and the gulf coast of Florida offer the most opportunity with average rainfall above 50” and 45” respectively [9]. With the whole world in mind this system could be an enormous provider of electricity. Places like Panama, where average rainfall approaches 100” per year and Columbia, where their average rainfall is between 200” - 300” per year, are areas where rainfall energy collection can be maximized [11].
With these averages of rainfall per year and a method to collect it, the potential for electric production is great. The possibility of supplementing the power supply and being able to save fossil fuels makes it a great idea for areas with large populations and a lot of rainfall, like
Seattle, Washington and Singapore in Malaysia. This is also a great option for places that can not be hooked up to a power grid, like islands in Indonesia, and isolated villages in the Amazon and Middle American rainforests which average 80 - 200” of rain a year [11]. Table 1 in the appendix shows the ten highest annual rainfall locations in the continental US and globally.
Collection Systems
In order to harvest energy from rain water, it needs to first be collected. There are many different methods of catching rainwater that are being used today. Water collection methods include funneling (gutters, roof design, etc.), holding (tanks, hoppers, reservoirs, etc.), and fog collection.

Funneling and Holding
One of the most generic methods of catching rainwater is the use of a gutter system. Such systems allow for maximum runoff funneling. Other forms of catchment include rain barrels and holding tanks. Rain barrels are normally used to collect rain water and then syphoned out for use in gardening or other outdoor applications. A holding tank is an accumulation device which stores water until it is needed for other uses. Another potential funneling device is roof design. A flat roof has more potential to puddle water than a sloped or lofted roof which would affect the amount of runoff that could be extracted during the period of rainfall. Some situations call for minimal runoff during the rainfall period such as in large cities and urban areas [7]. Some runoff minimization methods that have been implemented in the past include green, gravel top, and other types of substrate roofs. Green roofs consist of a vegetation layer, a substrate layer (where water is retained and vegetation is anchored), and a drainage layer (to evacuate excess water).
Traditional style roofs are generally covered with a shingle layer and are generally sloped at angles ranging from 0 to 84° [7]. Figure 1 in the appendix shows that the roof design plays a major role in the annual runoff. Traditional style roofs have the highest annual run off and would be most beneficial for a rainwater collection system.
Fog Collectors
Fog collectors are generally utilized in geographical areas that are generally between 600 and 1000m and with high precipitation averages such as the northern coast of Chile [10]. Fog collectors are used to capture precipitation from the air and funnel it through a series of tubes which is then distributed to local villages for non-potable use. It is to be noted that these villages sit at a lower altitude than the collectors; this allows gravity to aid the flow of the collected

water. A typical fog collector is comprised of a large nylon sheet stretched out over a rectangular frame which has horizontal troughs made of PVC tubing with slits for precipitation runoff. The size of the collector can vary depending on the needed output. An experiment done in El Tofo,
Chile used a 90m
2
collector which harvested as high as 4.3 L/m
2
per day during the month of
September in 1985. Such systems are relatively cheap to produce. Most systems of this size cost about $285 [10].
Pipe Corrosion
A problem that could be run into is the issue of acid rain. Normal water has a pH value around 7-8, whereas rainwater has a pH value of about 5.7 due to the presence of carbonic acid in the atmosphere [25]. This acidity in rainwater could be a problem for the piping used in this project, since acidic water could lead to corrosion. To minimize corrosion of pipes and equipment, utilities add lime to neutralize acidic water. Adding lime to a water supply is not a permanent solution, as acid rain is caused by many other factors than can be corrected in this project [24]. However, implementing the addition of lime could minimize the acidity of the rainwater, and therefore increase the life of the pipes [23]. Another solution could be to use a non-corrosive pipe, such as PVC.
Power Generation
After water is collected and stored, its potential energy must be converted to electricity.
The way to convert the potential energy from water into electricity is to run it through a turbine generator. A basic understanding of how a turbine generator works is essential for extracting energy from rainwater.

Expanders
An expander is a turbine or other system engine through which a pressurized liquid or gas is forced so that work is produced for use in an alternate application. In the case of gasses, expanders can also extract the work done by the expansion of gas such as in a combustion cycle in a piston cylinder. Other examples of expanders include gerotor pumps, scroll expanders, radial turbines, axial turbines, and drag turbines such as the simple water wheel.
In the process of selecting the right type of expander to use for a project involving the conversion of rain potential energy to electricity or other work, the choice can be narrowed by exploring the efficient uses of each type of expander. In his 2001 thesis, “Evaluation of
Expanders for use in a Solar-Powered Rankine Cycle Heat Engine”, Jon Johnston provides a depth of information comparing different types of expanders [4]. For his application, he was testing the use of these expanders in low to medium temperature organic rankine cycles operating between 70 - 350°F. As can be seen on the graph provided in the appendix, Figure 3, the efficiency of several different types of expanders depends on the specific diameter of the pipe and the specific speed at which the fluid is flowing through the pipe.
From this data, it can be determined that Axial and Radial type turbines may require a dynamic flow at a greater velocity than could be achieved from accumulated rain. Also, the cost of these types of expanders would be prohibitive to a smaller scale project because it would probably not be cost effective to only run it periodically with rainfall. Instead, the graph shows that at medium diameters and fluid speeds, Drag Turbines and Rotary Piston Expanders may be more efficient for this type of project [4]. Also, at larger diameters and slower speeds, Piston
Expanders may work as well. The most feasible expander to work with would be the Drag

Turbine. The Drag Turbine is a standard turbine that uses the force of a flowing fluid to generate work. The most basic example of a Drag Turbine is a water wheel, which has been used for centuries. The Drag Turbine would be a very good selection for this project because it has been proven to be an effective method for generating work from low temperature liquids, including water, and would be very adaptable to changes in project constraints.
Example diagrams of each type of expander discussed can be referenced in the Appendix
(Figures 4 -9) and are delineated as follows: Figure 4, the Piston Expander can be used in a combustion cycle or other type of low velocity, high pressure cycle. The reciprocating piston turns the crankshaft which generates work. Figure 5, the Rotary Piston Expander has a loose internal gear that turns about the fixed external gear as the flow of fluid from the intake is expanded to the outlet. An example of a Rotary Piston Expander is the Wankel engine used in several Mazda cars [6]. Figure 6 shows a Scroll Pump cycle, which compresses a gas or liquid when work is imputed, however by reversing the process, the fluid would instead be expanded to generate work. The expander uses a fixed scroll and an orbiting scroll. The orbiting scroll is moved in a circular motion that allows pockets of the working fluid to expand outward as it cycles and generates work. Figure 7 and Figure 8, the Radial and Axial Turbines, are both examples of a high velocity expanders that would have a prohibitive cost for the nature of a small scale project. The picture for the axial turbine shows the reverse cycle, an axial turbine engine, where work is an input to compress the working fluid (air) to create thrust instead of expanding the fluid to generate work. Figure 9, the Drag Turbine, is an example of an expander that would be an appropriate selection for a small scale rain collection project. The figure shows a wheel and shaft with exposed blades, however, the wheel and blades may be enclosed to

prevent the working fluid from being leaked from the system. Other examples of Drag Turbines are windmills, and the common water wheel [4].
Pico-hydro Power
Pico-hydro power is the collection of electric power from water flow amounting to less than 5kW. Generally this form of power production is used from streams or rivers in developing countries that cannot afford full scale power plants. The amount of electricity that Pico-hydro power produces is enough to power a television and several light bulbs for approximately 50 households [13].
One of the most efficient turbines for extracting Pico-hydro power is the Pelton turbine, or impulse turbine. A nozzle takes the water from the collection bin and increases the velocity.
The momentum of the water jet is absorbed by the runner of the turbine, which rotates the turbine. If the velocity of the water leaving the runner is nearly zero, then almost all of the kinetic energy of the jet will be transferred into mechanical energy of the turbine, which results in a higher efficiency. Several developing countries have already implemented Pico-hydro stations to generate electricity. Kathamba, a small site in Kenya, produces about 1.1kW from a
Pico-hydro plant using a Pelton turbine directly-coupled to an induction generator. The flow rate into the turbine is 8.4 L/s with a net head of 28m. This plant powers 65 households within a
550m radius, and supplies 230V to each household, enough for two energy saving lamps and a radio [5].
Piezoelectric Power
Certain crystals have the ability to create electricity when mechanical stress is applied to them. A few examples include quartz, topaz, sugarcane and tourmaline. Normally a

piezoelectric crystal is electrically neutral. When the crystal is stressed the atomic structure is deformed, upsetting the balance of charges and creating a voltage. A basic piezoelectric system has two plates with crystals between them. When pressure is applied to the plates the crystals deform which creates electricity. A piezoelectric system could be used to generate power from rain drops hitting it. One rain drop can generate anywhere from one microwatt to twelve milliwatts. This small amount of power that is possible to generate isn’t significant enough to be used for energy extraction from rainfall [2].
Reuse of Expelled Water
Evaporative Cooling
Evaporation is a constantly ongoing process. When dry air passes over water, some water is absorbed by the air. Energy from the air is transferred to the water in order to for a phase change to take place. Since energy moved from the air to the water, the air is now cooler than it was before. An evaporative cooler utilizes this principle by drawing hot air in through dampened pads and then circulating the cooled air with a fan. They are also commonly known as swamp coolers because they add moisture to the air. The hotter and drier the air is, the more water an evaporative cooler can absorb. A small, but consistent water source must be supplied to the pads to keep them damp. Also since water is constantly leaving via evaporation, some kind of valve is necessary to fill the unit back up with water. Figure 10 in the appendix demonstrates how an evaporative cooler works. Cooling an area by way of evaporative cooling is generally much more cost effective than doing so with refrigeration air conditioning. The main disadvantage of evaporative cooling is that there must be dry air present for it to work well. Evaporative coolers are most commonly used to cool homes in place of air conditioning. Some homes that have

evaporative coolers also have air conditioning units in case the relative humidity rises, making the swamp cooler less effective [1].
Non-potable Water Use
Collection systems have been implemented in Danish households in order to use the collected rainwater for non-potable water needs such as toilet flushing, washing machine use, and garden hose use. Figure 2 in the appendix shows a typical system schematic for rainwater collection. Water is brought into a holding tank from a gutter and it is filtered and pumped throughout the house for various needs. This system is shown to have a 0.68 replacement ratio when used for households as shown in Table 2 in the appendix. These collection systems have an average installation cost, including materials, of about 15,000 DKK or $2800.00 U.S [8].
Previous Attempts at Rainwater Energy Conversion
A senior design group at the University of Illinois at Champaign-Urbana designed a rainfall energy conversion system. They collected rainfall and sent it through a turbine with an electric control system. However, the design was extremely basic and there were not very many calculations reported in the proposal. In their proposal there were several discrepancies, including; missing/incorrect calculations, no system schematics, and the fact that their design was very simplistic, given that the turbine was homemade, using measuring cups [3].

Appendix
Table 1
HIGHEST ANNUAL RAINFALL AND THEIR AVERAGE HUMIDITIES
US (lower 48 states)
1 Mobile Alabama
Inches Humidity
67 75.5
2 Pensacola Florida 65 74
3 New Orleans Louisiana 64
4 West Palm Beach Florida 63
5 Lafayette
6 Baton Rouge
7 Miami
8 Port Arthur
9 Tallahassee
10 Lake Charles
Louisiana 62
Louisiana 62
Florida
Texas
62
61
Florida 61
Louisiana 58
76
72.5
77
76.1
72
79.1
73.5
77
Globally
1 Lloró, Colombia
2 Mawsynram, India
Inches Humidity
523.6
467
3 Mt Waialeale, Kauai,
Hawaii, USA
4 Cherrapunji, India
460
5 Debundscha,
Cameroon
6 Quibdo, Colombia
425
405
354
7 Bellenden Ker,
Queensland,
Australia
340
8 Andagoya, Colombia 281
9 Henderson Lake,
British Colombia,
Canada
10 Crkvica, Bosnia
256
183
85
78
75
82
88
88
73
90
78
70
Table 1 shows the average rainfall and humidity data for the cities with the most annual rainfall in the continental US and globally.
Figure 1
Figure 1 shows the annual runoff percentage for different roof types [7].

Figure 2
Figure 2 shows the schematic for a rainwater collection system for non-potable water use [8].
Table 2
Table 2 shows the replacement ratios for different living quarters [8].

Figure 3
Figure 3 shows the efficiency map of different expander types [4].
Figure 4
Figure 4 shows a typical piston-cylinder assembly[16].

Figure 5
Figure 5 shows a typical gerotor and rotary piston expander assembly [18].
Figure 6
Figure 6 shows an example of a scroll expander [14].
Figure 7
Figure 7 shows a typical radial turbine [19].

Figure 8
Figure 8 shows a how a typical axial turbine works [15].
Figure 9
Figure 9 shows a typical drag turbine [17].

Figure 10
Figure 10 shows a typical evaporative cooling system [1].
Table 3
Table 3 shows comparisons of various water collection systems [20] [21] [22].

References
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